Minimizing groundwater nitrates with proper fertigation

Even distribution of water and fertilizer are key to reducing nitrates and saving water.

Dennis Pollock | May 23, 2013

As many of California’s growers face expected tighter regulations on nitrates in groundwater, Fresno State University unrolled a series of ambitious seminars on water use efficiency, concentrating in the first workshop on fertigation and how to minimize the amount of nitrates entering the groundwater.

The seminar opened with an outline of the serious health threats posed by nitrates in the drinking supply of the San Joaquin Valley. It concluded with some tips on how to target the root zone of plants with needed water – and accompanying nitrogen – and how to avoid going past that root zone, how to protect water sources and how to prevent backflow and spills of fertilizer.

Bill Green, an educational specialist at Fresno State, said that some regions other than Fresno County, which leads the nation in agricultural production, have more stringent regulations related to pollution from nitrates.

But aside from looming regulations, he believes it is in the interest of growers and their advisers to take steps to greater efficiency as has been done in regions that include parts of the Salinas Valley, Ventura County and Nebraska.

Green and other presenters at Fresno State said better efficiencies at delivering nitrogen where it’s needed can save money and contribute to sustainability of farming operations, things that are in the self-interest of growers as well as regulators.

“It’s the right thing to do,” Green said.

The Fresno State event was sponsored by the California Department of Food and Agriculture and its Fertilizer Research and Education Program. It was held at the AgWaterEnergy Center, which is part of the Center for Irrigation Technology.

Upcoming CIT seminars, most of them from 9 a.m. to noon, include workshops on water use efficiency on the farm for small farm operations in Del Rey May 22; Wateright for specialty crops May 23 at Fresno State; air injection June 6 at the Center for Irrigation Technology; fertigation on a production farm in Selma June 13; fertigation for small farm operations July 11 at the CIT; water use efficiency in almonds June 23 at the Fresno State farm and water use efficiency for citrus at the FSU farm Aug. 22.

Green used equipment at the university to show how to protect the water source, how to install an automatic system to shut it down when it is not working properly and how to keep pressurized irrigation system water from flowing back into the fertilizer supply.

He was not bashful about acknowledging his own mistakes as a farmer, including a time when fertilizer spilled from a pumping system’s fertilizer supply resulting in some trees being killed in a peach orchard.

And his demonstration at the university including showing what can happen when nozzles become clogged. His emphasis was on the even distribution of water.

Distribution vital

He said distribution uniformity of water – and with it fertilizer -- is a key and results in saving water, fertilizer and energy.

Uneven distribution can result from poor design of a system, differences in elevation and poor maintenance that results in leaks, plugged emitters, pressure valves not calibrated properly or poor filter maintenance or design, he said.

Inefficient systems may result in delivering too much water and fertilizer to some parts of the field, pushing nitrates past the root zone and into groundwater, while skimping on nutrients and water in the root zones of other plants.

Green recommends auditing the system to determine distribution uniformity levels.

Simply using check valves that cost as low as $3 can be important for a watering system, he said, adding that a good injection system should include backflow prevention and automated system shutdown in the event of a pressure or flow loss.

An injection line check valve will keep reverse flow from the pressurized irrigation system from overflowing the fertilizer supply tank, Green said.

Presenters at the seminar armed participants with web sites that can serve as resources as they fine tune their fertigation systems so as to deliver nutrients to their crops through their irrigation lines without sending those nutrients past the root zones.

For example, Sajeemas “Mint” Pasakdee, soil scientist at the university, cited a web site that can be used to help determine how much “plant available nitrogen” may already be in the soil, thereby cutting down the amount of nitrogen needed to feed the crop.

Soil tests can cost from $20 to $25, she said, adding that part of knowing the soil involves collecting samples, understanding its texture by feel and recognizing that soils vary on the ability to hold water.

Pasakdee’s pointers were aimed at development of nutrient management plans that are important to monitoring and quantifying fertilizer inputs and outputs and maximizing fertilizer use efficiency, thereby protecting groundwater and soil efficiency. She said maintaining soil health is important to sustainability and the livelihood of future generations of farmers.

In addition to knowing the soil, the grower should also “know the crop,” for example how much of crop nutrients are removed by it and the periods when it is most in need of those nutrients.

She said a worksheet developed by the U.S. Department of Agriculture can be used to calculate nutrient management and nitrogen in storage by following a link to http://plants.usda.gov/npk/main.

Know the water

And Pasakdee said growers also need to “know the water.” She recommends testing irrigation water to determine nitrate and salinity levels. Groundwater, she said, has “somewhat higher” nitrogen levels.

Pasakdee said it’s also important to “know your fertilizer,” the types and sources being applied and the methods of application.

She cited a “4R nutrient stewardship concept”: using the right source (whether soil or foliar); using the right rate (perhaps splitting applications over time); applying to the right place (the roots); and applying nutrients at the right time.

Kaomine Vang, project manager at CIT, talked of the benefits of using fertilizer and of the effects on drinking water, which is a significant health concern in San Joaquin Valley and elsewhere.

He said one way to prevent leaching of water and nutrients is to use soil moisture sensors to monitor water movement through the soil.